Compression test part 2 - results not good!

[oldgreyandslow]

Followed the advice given in previous posts and the results were:

#1 8 bar, #2 just slightly under 8 bar, #3 7.3-7.5 bar, #4 just slightly under 8 bar

Next put a few squirts (3squeezes on the oil can approx 1 teaspoon ish) of oil in through the plug hole and the results were:

#1 10 bar, #2 11 bar, #3 9.5-10 bar, just under 11 bar

I assume this points to worn rings, so what's the best solution? Replace the engine or did I do somthing wrong in the testing?

Anyone want a bike with a fucked engine?

[Neosophist]

Yep... Worn rings on cylinder #3.

The oil acts as a seal for the rings... this will be why your bikes smoking an awful lot.. the blowby will also contaminate the oil and use oil faster (these bikes don't usually use any oil)

You can either strip it down and inspect the damage and replace the rings (depends on if the bore is worn, if its the bore not the rings then the barrels scrap and as its part of the head a new engines pretty easier)

Depending on what you find in there it might be more than just rings (bearing shells etc so could be pretty pricey)

Might be better off sourcing a cheap motor and keeping / breakign that one for spares... (i'd start with a stripdown and see what its like inside.. check bearings and journal clearnaces and see what the bore of #3 looks like!) You'll soon get an idea of if its servicable.

Sounds bad though

[80sman]

I have a question?

All the cylinders are rising by 2-3 bar on the leak down test with #3 being still low. Doesn't this point to valve seals?

If it was rings wouldn't the compression equalise with the oil?

Just curious, as I don't know?

[Neosophist]

Not necissarly,

Dont' forget the engine is cold so things havn't fully expanded (gives an extra bit of compression) the oil coats the cylinder bore helping the piston rings to seal.

If you have worn rings they might not even seal properly with the oil in there, which is probably why this cylinder is low.

If the compression was down to valve clearances being to low (keeping the valve open) then the oil wouldn't make any difference to compression reading.

Since the oil makes it go up the rings are at fault.. since the compression is still lower than the others.. which I presume is what you mean by 'equalise'

The oil is either not giving a 100% good as seal as the other cylinders (would be most likely) but there is still the possibility of a valve having slight blowby and loosing the extra bit of compression.

However, since the rings are damaged and need to be inspected to see if they can be replaced you can inspect the valves while the heads are off. Anytime I have to do headwork like that I always clean up the valves and re-lap them in to ensure they are sealing 100%, this can be done at the same time as the rings :-)

Hope that makes sense

[oldgreyandslow]

Quick update

I was concerned that my plastic washer, and the difficulty in getting oil into #3, it was the last one I did, may have given a false reading so I did it again with the adapter and no washer it was 8 bar initially and 11 after the addition of oil.

So they are all pretty much the same 8 bar cold and 11 when oil added, so I guess all 4 have shagged rings?

What concerns me most is that when I went to see the bike, prior to nuying the thing (MISTAKE!) just over three weeks ago it didn't smoke, and it didn't seem to be smoking on the ride home and later that day when I was out and about on it, the following week the reg/rec failed and the week after it cut out and then that's when the smoking issues started, or at least became apparent. I wonder what the bloke selling it did to mask the smoke, assuming he is a dodgy git, or did I do something to it?

[porndoguk]

Quick update

I was concerned that my plastic washer, and the difficulty in getting oil into #3, it was the last one I did, may have given a false reading so I did it again with the adapter and no washer it was 8 bar initially and 11 after the addition of oil.

So they are all pretty much the same 8 bar cold and 11 when oil added, so I guess all 4 have shagged rings?

What concerns me most is that when I went to see the bike, prior to nuying the thing (MISTAKE!) just over three weeks ago it didn't smoke, and it didn't seem to be smoking on the ride home and later that day when I was out and about on it, the following week the reg/rec failed and the week after it cut out and then that's when the smoking issues started, or at least became apparent. I wonder what the bloke selling it did to mask the smoke, assuming he is a dodgy git, or did I do something to it?

Sadly this sort of SHITE is on the market (it should say in the auction) "makes for a perfect use for selling a fucked car or bike to an unsuspecting buyer, where in a 100miles times the engine will smoke like a good un"

http://www.ebay.co.uk/itm/HOLTS-PISTON- ... 27b8e49e6c

[oldgreyandslow]

Sadly this sort of SHITE is on the market (it should say in the auction) "makes for a perfect use for selling a fucked car or bike to an unsuspecting buyer, where in a 100miles times the engine will smoke like a good un"

http://www.ebay.co.uk/itm/HOLTS-PISTON- ... 27b8e49e6c

I thought something like this could be it!

I'm sorely tempted to go round to the blokes gaff and kick the fuck out of him, twice

However I have now fallen in love with this sorry piece of shit and am determined to return it to its former glory, cost IS an issue, time isn't. I've resigned myself to not riding the old girl this summer, but next year is the plan, It will work again eventually, but FFS why oh why did I not spot this fucking lemon!

[Neosophist]

Since the compression is equal on all cylinders that sounds fine to me.

8-11 bar is good compression.

Service it and just give it a good ride, see if it stops smoking.

It could be the valve-stem seals leaking a small amount of oil into the cylinders causing the smoke... run the bike for a while and keep an eye on the oil level, if it's dropping then you might have leaky valve stem seals... if you shine a torch into the inlets with the carbs off have a look at the valve stems, are they clean / sooty or wet?

[oldgreyandslow]

Since the compression is equal on all cylinders that sounds fine to me.

8-11 bar is good compression.

Service it and just give it a good ride, see if it stops smoking.

It could be the valve-stem seals leaking a small amount of oil into the cylinders causing the smoke... run the bike for a while and keep an eye on the oil level, if it's dropping then you might have leaky valve stem seals... if you shine a torch into the inlets with the carbs off have a look at the valve stems, are they clean / sooty or wet?

I'm now confused, sorry. I thought if I did a compression test and added oil and the compression went up it indicated worn rings and a knackered engine? Not the case then?

[80sman]

My understanding of it is that adding oil improves sealing around the rings in any condition, so nope, I wouldn't have said it's a certainty that the rings are knackered. Just check whether 8 bar is good for the nc engine. I think that's around 120psi......

A quick google shows 120psi being good for an NC, personally, I'd just ride it for a while and see if it clears up.

You haven't got water in the fuel have you? Gives you lots of white smoke?